Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $42.63   10.210%   $46.9825   $46.98   $47.00   $47.00  
  Purchase #2 $244.63   12.459%   $275.1085   $275.11   $275.10   $275.10  
  Purchase #3 $143.43   9.855%   $157.565   $157.57   $157.55   $157.60  
  Purchase #4 $167.52   9.353%   $183.1881   $183.19   $183.20   $183.20  
  Purchase #5 $78.99   12.705%   $89.0257   $89.03   $89.05   $89.00  
  Purchase #6 $131.43   8.768%   $142.9538   $142.95   $142.95   $143.00  
  Purchase #7 $88.36   4.347%   $92.201   $92.20   $92.20   $92.20  
  7 purchase totals = $896.99       $987.0246   $987.03   $987.05   $987.10